For example, as shown in Japanese Patent Application Publication No. 2004-282989, an axial air-gap electronic motor is formed so that a rotor is arranged along the axis direction of a rotor output shaft opposedly on both sides (or on one side) of a disc-shaped stator with a predetermined gap being provided therebetween. The axial air-gap electronic motor has an advantage of being capable of being made small in size because the axial length thereof can be shortened.
The stator has a plurality of stator cores (core members), and the stator cores are arranged in an annular shape around a bearing portion provided in the center, and are molded integrally by synthetic resin. The stator core for the axial air-gap electronic motor is formed by laminating a plurality of core sheets along the radial direction. To increase the torque, the stator core is contrived to increase the teeth area by being formed into a trapezoidal shape such that the width in the circumferential direction increases gradually from the center side to the outside.
Also, in some stator cores, a configuration also has been proposed in which the side surface in the circumferential direction (slot surface) is provided with a skew to restrain the occurrence of cogging torque. However, the manufacture of the stator core for the axial air-gap electronic motor has problems described below.
In the case of the stator core for the axial air-gap electronic motor, unlike the inner rotor electronic motor, the stator cores are laminated along the radial direction. Therefore, since the teeth surface must be formed into a trapezoidal shape, the shape of core sheet must be changed one by one. Also, since the shape must be changed every one sheet, blanking dies corresponding to the number of core sheets are needed, which increases the production cost.
Also, in order for the slot surface to take a slantwise shape, the core sheets must be laminated while shifting slightly one by one, which takes much time and labor. Further, since the core sheets are laminated in a shifted state, the positioning requires a technique.